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01' Cavalier - Issues Intermittent

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  • 01' Cavalier - Issues Intermittent

    Started off being that the car had some "hesitation" first drive in the morning after a wait until temp reached full 195 before leaving for work, it has been a flawless ownership and paid for a new engine to be installed by GM dealer. (wanted to keep car for a LONG time)

    Now, I have new issue. I need help understanding what can be the problem of the car running fine on CNG & Gasoline but lately it has not wanted to "start" on CNG at all, I would then have to pull bumper off, unplug and plug back in the AF ECU, the car will start on CNG.

    I have no DTC's present on Vehicle with Scan Tool but my ScanTool does not have the "Special AF ECU Mode" so I cannot tell you about DTC's on AF ECU.

    So I also noticed too that I once was able to start car on Gasoline by the FIL (Fuel Indicator Lamp) on the dash, but now if I try; the fuel gauge changes to the Gasoline side (level) but it DOES NOT switch to Gasoline by the FIL any longer. I am suspicious of this as I believe it is a symptom of what the problem is.

    To recount what is happening now;

    1. Car runs flawless with no DTC's and is a new engine
    2. Runs on BOTH CNG/Gasoline
    3. Car now lately has spontaneously quit starting on CNG without pulling 20AMP CNG Fuse; it will start then on Gasoline (you cannot switch by FIL on dash anymore)
    4. When I pull the AF ECU Blue and White off and then run on Gas, shut off and then plug back the Blue/White the car will now Start on CNG without issue.
    5. There has been one occasion that the car "died" while driving on CNG and would not restart on CNG, had to pull 20AMP Fuse; started and ran fine on Gasoline.

    I have paid over 200$ for no luck at GM Dealer to troubleshoot this bizarre issue, Dealer stated that GM Techs were not helpful either on this.

    Your assistance would highly be appreciated

  • #2
    Re: 01' Cavalier - Issues Intermittent

    Sounds like a mess to sort out. First, lets confirm what happens when you try to start the car. With CNG in the tank, you should look at the fuel indicator lamp and listen for the high pressure lockoff valve to "click" when you turn the key to "on". The indicator lamp should come on for a couple of seconds and then go off. When you start the car on CNG the bulb in the fuel indicator should stay off indicating CNG operation. If the bulb is illuminated, then you are running on gasoline. The car should switch to CNG after a short drive after certain conditions are met. If the AFECU isn't getting power, the bulb check will not happen and no CNG operation will occur. I am sure you know all this but just check to see what is going on at engine start. I think you should look carefully at the wiring around the AFECU and the four relays located next to it. The fact that you can remove the AFECU connectors and then get the car to run on CNG makes me think that something is going on in those connectors or the connectors going to the relays. Your fuel indication being wrong is a product of one of those relays failing to operate when there is a CNG signal from the AFECU. Check all the pins in the AFECU connectors and the relays--check the harness where it goes through the frame and around the battery for any cuts or chaffing. Look at (and clean) all of the grounds. Report back .
    Last edited by siai47; 06-22-2009, 05:33 AM. Reason: spelling

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    • #3
      Re: 01' Cavalier - Issues Intermittent

      lets confirm what happens when you try to start the car. With CNG in the tank, you should look at the fuel indicator lamp and listen for the high pressure lockoff valve to "click" when you turn the key to "on". The indicator lamp should come on for a couple of seconds and then go off. When you start the car on CNG the bulb in the fuel indicator should stay off indicating CNG operation.
      Confirmed; all the above is exactly what occurs and has been verified

      What is strange on this whole issue is that if you turn the ignition on and try to start car; it will "act" like it wants to ignite twice but then just sit and crank without any ignition attempts of starting the engine. But initially it will "act" like it wants to start two times of a "normal" crank, then just cranks until you stop and do it again... repeat... repeat.. but will not start until you pull fuse for cng, pull battery or AFECU and then will start on CNG fine..


      If the bulb is illuminated, then you are running on gasoline. The car should switch to CNG after a short drive after certain conditions are met. If the AFECU isn't getting power, the bulb check will not happen and no CNG operation will occur.The "bulb" on the Fuel Indicator Light remains OFF when running on CNG, FIL will be "ON" when running off of GASOLINE; correct and that is the way the car behaves.

      Interesting is when you disconnect the battery, the AFECU will "reset" and the car will start on CNG, run for a undetermined distance and then "die" out or if you turn the ignition off it will NOT start again on CNG; disconnect AFECU or Disconnect Battery, reconnect and the car will run fine for a while and start up "IMMEDIATELY" with no drive degradation.

      Again, no ECU DTC's present on ODB or AFECU when all this occurs


      I have checked in as much detail as I could of the harnesses for wire chaffing, etc. and have not found anything.
      Last edited by CNG4Sure; 06-26-2009, 01:39 PM.

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      • #4
        Re: 01' Cavalier - Issues Intermittent

        You've looked at about everything I have asked you to. I am interested about your paragraph in your original question that said something about changing operation by pushing the switch that has the FIL in it. It sounds like you are saying that the vehicle would switch from gasoline to CNG or vise versa. If that is what it has been doing that would be really strange as the switch only determines if you are reading CNG or gasoline fuel level---it will not change the fuel type the engine is running on. Also, with the ignition switch off, the AF ECU receives 100% of it's power from the 20 amp CNG fuse--therefore, pulling that fuse totally powers down the ECU and will cause the same type of reset that you would have if the battery was disconnected. If you are trying to read DTC's, some scanners will read the AF ECU codes, others will not unless the AF ECU is running the vehicle. In any event, the AF ECU must be powered for the codes to be read even by the Tech2. Did you confirm the connections to the four relays above the AF ECU are in good shape? The relay closest to the front of the car controls the fuel gauge, next is the lock off relay, next is the AF fuel pump relay, last is the ignition relay. All the relays are the same so you could swap the connectors around and see if that changes your problem. Try to get someone with a Tech2 to verify there are no DTC's stored in the history file for the AF ECU and try to view some of the data stream from it if you can get the engine running on CNG. If there are actually no DTC's stored, it still sounds like there is a wiring issue somewhere, if not, it is possible the AF ECU is biting the dust. Two final things (as this is an issue that affects starting on all pre 2003 Cavaliers) make sure that the lockout valves are opening (and the LPL is the most suspect). There is a TSB about this when you have hard starting issues. Last point, you say when the car will not start on CNG, no matter how long you hold the key to start (at least 8 seconds) it will not try to start on gasoline. This changeover is programmed into the AF ECU and if it is not working it starts to point again to ECU failure.

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        • #5
          Re: 01' Cavalier - Issues Intermittent

          It sounds like you are saying that the vehicle would switch from gasoline to CNG or vise versa

          I guess I mistook that FIL switch and experience with confusion, When I had depressed and the fuel level indicator would switch over to the appropriate fuel, I could have been absolutely positive that the FIL was "ON" and it did or was running on Gasoline; I may be mistaken on this.



          AF ECU receives 100% of it's power from the 20 amp CNG fuse--therefore, pulling that fuse totally powers down the ECU and will cause the same type of reset that you would have if the battery was disconnected.

          Correct!; we are saying same thing



          If you are trying to read DTC's, some scanners will read the AF ECU codes, others will not unless the AF ECU is running the vehicle. In any event, the AF ECU must be powered for the codes to be read even by the Tech2



          Correct; I am unable to read AFECU PID's on my scantool; I don't have access to one either, just a Sunset..



          Did you confirm the connections to the four relays above the AF ECU are in good shape? The relay closest to the front of the car controls the fuel gauge, next is the lock off relay, next is the AF fuel pump relay, last is the ignition relay. All the relays are the same so you could swap the connectors around and see if that changes your problem.



          Yes, all looked fine and all relays behaved perfectly.


          How to test the LPL? I have been having to crank for upto 8-15 seconds, Sounds like I need to look into it and see if that would be the cause of my hard start; tech told me some TSB about the NG being in manifold causing the need to crank to clear out, etc.


          Found my issue; faulty grounds; cleaned, protected, torqued down and now all is well, except my Hard Start issue.

          I rewrapped all wires with new tape, sealed, cleaned, etc. and re-secured harnesses, re-tied all, checked all connectors, etc. and glad I did it as there was some chaffing that would have been a disaster so this was a good routine to maintenance the system...

          Thank you for your help!

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          • #6
            Re: 01' Cavalier - Issues Intermittent

            UPDATE**********

            Issues started to come back again.... Died right at intersection, weird issues of dying... Checked and Checked again and again my wire harnesses, etc.

            Solved.... How?

            Removed battery, took air filter container out, removed bottom of fuse block assembly (the back "clipped on") and found corrosion and rust everywhere on the "positive bus" and connection from battery...

            Took wire brush and sand paper to BUS, connection, cleaned positive cable/ buses and then secured again, double checked negative/ grounding on engine and battery... Wrenched down and secured connections again and fired up without any issue so far and no intermittent dying "YET"


            Will update this post again if there is any further "weird" dying issues..

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            • #7
              Re: 01' Cavalier - Issues Intermittent

              I recently had problems with that same fuse block. My AC/Heater blower was shutting down intermittently. I traced the issue to the blower relay on that block and I found that one of the clips on the block that hold the legs of the relay was loose. If you find a loose one you can remove them through the bottom of the block. They are crimped to the wire. I had to compress the clip to hold the relay tighter and then all was ok. I've had no problems for several weeks now. The block seems to be a cheap flimsy thing...
              Last edited by rguzek; 10-28-2009, 05:50 PM.

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              • #8
                Re: 01' Cavalier - Issues Intermittent

                I used "YET" and thankfully that is the truth... Ran great for one solid week and then again, died right in middle of driving.. I have had in to GM dealers and they are blindly guessing and have had no "resolve" to my "intermittent" issues.

                Here they are again for clarification.

                Symptoms:

                When all was great there had been a "surging" in the engine after driving for 5 mins... You could feel surging but that would go away.. Only occur initially.

                Car became "hard to start" and GM gave a update bulletin disclaimed that there was no issue and to expect a 12-15 sec turn over before ignition; their belief of my issue was that the gas was still not cleared out..

                Then finally the bullet, car would stop running "for no apparent reason"...

                When I started posting this here and after many months here is what happens.

                1. Start car on CNG, runs till dies...

                2. Try to start and it will "act like it will ignite" but does not and will not start.

                3. Remove CNG fuse from block, start on GASOLINE

                4. Shut off car from GASOLINE and put fuse back in

                5. Car WILL START and RUN on CNG, until it dies (no set time, no set temp., could be 5 mins or can be 5 miles of driving or 10 miles)

                Key here is that I have had success unplugging all harnesses, tearing front off and inspecting AFU ECU, remounting, cleaning, securing all connections and then most recently cleaning and securing fuse block assembly.

                I noticed this time the stepper motor was HOT, is that normal? Could this be a multi symptom issue to many issues that was resolved over the last months of dedicated cleaning and securing and ultimately come back to a stepper motor on top of it?

                When the car surged it seamed to be a "fuel delivery" issue, if the Stepper motor was to get too hot, thermal shut down?

                I know the AF system runs off of the Negative side and have cleaned and secured all electrical to the best of my ability, now I am pulling at guesses.. I see no DTC's from the AFU ECU in the test prescribed above in this thread..

                One last thing.. Right before car dies, car has that "surging or hesitation" issue and then stops running..

                THe only things consistent here are my effort to find the issue, surging, fuse actions taken to get car running, dying... Every single time.

                All replies and ideas would be appreciated.
                Last edited by CNG4Sure; 11-02-2009, 09:10 AM.

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                • #9
                  Re: 01' Cavalier - Issues Intermittent

                  Update...

                  Car finally did start to stutter, jolt, run poorly on CNG or on Gasoline...

                  Finally after all this time.. The car is running better than ever, ended up being MAP sensor and O2 Sensor causing all kinds of "weird" issues.. Funny part was that the O2 was bad and still read frequency, the MAP was not entirely bad either but both read somewhat in "spec" on Tech2... After driving found lean and isolated, replaced both and now... No more dying, no more intermittent running issues, I don't have to play "switch" the fuse...


                  I truly hope someone profits from this long time post...

                  Take care...

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